The pyrolysis of
endothermic hydrocarbon fuel plays a vital role
in regenerative cooling channels. Based on previous experiments and
mechanism models of n-decane, and considering the impact of the secondary
reaction at high conversion, the present work establishes a cracking
reaction model of n-decane containing 16 species and 26 reactions.
One-dimensional plug flow reactor simulation verifies that the model
has high accuracy in predicting species distribution. The high-accuracy
model is applied to the computational fluid dynamics (CFD) simulation
of the supercritical cracking heat transfer, and compared with the
results of a one-step global model as the chemistry model. The results
show that the high-accuracy model is more accurate in terms of fuel
conversion, temperature, and product distribution. Furthermore, the
reasons for the difference of the two chemistry models in the CFD
simulation are analyzed from the perspective of chemical kinetics.
The new model generates more products of small molecules due to the
consideration of secondary reactions. However, for the one-step model,
it mainly cracked into large molecules even at high conversion. The
product distribution affects the chemical endotherm and then the fuel
temperature, which in turn affects the reaction rate and finally the
conversion of the fuel. In addition, pyrolysis affects the properties
of the fuel, which in turn affects the convective heat transfer. Among
the several influencing factors of heat transfer, the correction factor
of isobaric specific heat, which is the ratio of the specific heat
of fluid to the average specific heat, can well reflect the changing
trend of the convective heat transfer coefficient. The present work
demonstrates the important role of the kinetic model in the simulation
of the supercritical cracking heat transfer process, and the corresponding
methods can be used in the design of regenerative cooling systems.